1. Field of the Invention
The present invention generally relates to data communications, and more particularly to pre-emphasizing a data signal.
2. Description of Related Art
High-speed data transmitters often include circuitry for pre-emphasizing a data signal to compensate for transmission losses occurring in a transmission channel. The transmission losses include frequency dependent losses in amplitudes of the data signal. Before transmission, data is encoded in the data signal by using a voltage level to represent a data value of zero and another voltage level to represent a data value of one. After transmission at sufficiently high data rates, losses occur in the amplitude of the data signal at transitions between the levels. Additionally, losses vary across frequency components of the data signal, which affects the frequency bandwidth of the data signal. As a result of these frequency dependent transmission losses, the data signal is distorted after transmission. To compensate for these transmissions losses, the data signal is pre-emphasized prior to transmission.
One technique for pre-emphasizing a data signal involves emphasizing the amplitude of the data signal at each transition between levels to compensate for losses in amplitude that occur during transmission. Another technique for pre-emphasizing a data signal involves emphasizing selected frequency components of the data signal to compensate for changes in frequency bandwidth that occur during transmission. Although each of these techniques has been successful in some circumstances, improvement in pre-emphasis of data signals is needed because of an ever-increasing need for higher data rates in data signals.
In light of the above, a need exists for improving pre-emphasis of a data signal.